Linux.Desktop.Hacks [Electronic resources] نسخه متنی

Hack 39. Script Hacks with DCOP

Use the KDE scripting tool of choice to tweak
your desktop for maximum flexibility.

For most users, interaction with
the desktop is a simple process that is
limited to clicking buttons and typing things in from the keyboard.
Although fine for most cases, this normal form of interaction limits
what you can accomplish with an application, because you are
restricted to the program elements that the GUI has been designed to
show, and because complex or repetitive tasks require the user to
input every command himself. Many programs can be augmented with a
scripting tool to overcome traditional input methods.

Within the KDE feature set is a special tool called the Desktop
COmmunications Protocol (DCOP). This facility can access a number of
so-called "hooks" in KDE
applications that can allow programs to communicate with other
applications either remotely, with a scripting language, or from the
command line. DCOP essentially provides a means for you to hook
together graphical programs in the fine tradition that Unix and Linux
command tools can be connected with pipes.

DCOP is a tool that typically resides in the
developer's toolbox, out of sight from most users.
But DCOP is also a tool that you can use in everyday desktop
practice. Although hackers are animals that enjoy wallowing in reams
of code, a little GUI application is available, which nonhackers can
use as an interface to DCOP to facilitate the process of writing DCOP
programs. It is called KDCOP and you can start it by typing
kdcop into a console or in the Run application
dialog box (Alt-F2).

5.6.1. DCOP and Processes

Each KDE application that you are running on the system has a number
of DCOP "interfaces" that provide
methods for learning information about the application and adjusting
how it works. When you run KDCOP, each interface is displayed and you
can play with them inside the program. For example, run KDCOP and
then load a Konqueror browser. You will see Konqueror added to the
list of applications in the KDCOP window. You should also see a
number to the right of the entry, such as
konqueror-1377. This number relates to the process
number of the application. This number is added, because often more
than one process is running for each program at any one time. If you
click the Konqueror entry you are presented with a list of categories
that contain DCOP interfaces.

To test an interface, look in the category called
KonquerorIface and double-click the entry
DCOPRef createNewWindow(QString
url), as shown in Figure 5-3.

Figure 5-3. Browsing DCOP interfaces with KDCOP

Not surprisingly, this string creates a new window. The
QString url part in brackets
means you can pass the interface a web address or file location and
the interface will display that resource in the window. When you
double-click the interface, you are prompted for this value and then
Konqueror opens a new window with the requested URL.

You can tie DCOP functionality into a number of places. For example,
you can access a similar DCOP interface from the command-line shell
with:

foo@bar:~$ dcop konqueror-1377 KonquerorIface openBrowserWindow http://www.oreilly.com/

Notice how you need to specify the process number of the application
within the application name (your process number might be different
from mine). This is so you can probe the correct Konqueror process
and open a new browser window.

5.6.2. Write a DCOP Shell Script

The true power of DCOP
comes into its own when you start
writing shell scripts. As an example, imagine that numerous
applications are in use across all your virtual desktops. Things are
getting a little messy on these desktops and you want to tidy up. You
can solve this problem by writing a little script that switches to
each desktop and runs the cascadeDesktop
interface, which organizes the windows in a cascaded order.

To create this script, create a new file called
cascade.sh and add the following code:

#!/bin/bash
for i in seq 1 5:
do
dcop kwin KWinInterface setCurrentDesktop $i
dcop kwin KWinInterface cascadeDesktop
done

This code creates a bash for loop that loops four
times (for the number of desktops). Inside the loop, it sets the
current desktop to that of the loop number, and then it issues the
cascadeDesktop interface command.

To run the script, you need to turn on the execute bit on the file:

foo@bar:~$ chmod a+x cascade.sh

Then you can run the script with:

foo@bar:~$ ./cascade.sh

As another example, say you want to receive an email when your friend
Nick logs on to your instant messenger network. This could be
particularly useful if you leave Kopete (the KDE instant messenger)
running at home and you want to know when someone is online while you
are at work. You can accomplish this with the following script:

#!/bin/bash
nick=$1;
echo Waiting for $nick
while ((`dcop kopete KopeteIface reachableContacts | grep -c $nick` == 0))
do
sleep 10
done
echo Sending message
mail -s "$nick is online" 

Save this script to a file such as immail.sh and
run it, like so:

foo@bar:~$  ./immail.sh bob

This script works by first making the command-line argument available
as the $nick variable. After this, a
while loop is started that uses
grep to search for the chosen
nick in $nick within the
output of the reachableContacts interface in
KopeteIface. Nick is not online, so the process
will just sleep for 10 seconds. When Nick does come online, an email
is sent to